DACs are widely implemented in integrated circuits (ICs). For example, DACs may be used in cellular base stations, test equipment, waveform generators, and in wireless communication systems. Binary-weighted DACs include a number of taps that receive different binary-weighted currents and a series of switches coupled to the taps. The opening and closing of the switches are controlled by an input code, which in turn controls the output current.
Thermometer codes have been implemented to reduce transient glitch energy problems associated with switching in binary-weighted DACs. U.S. Pat. No. 5,568,145 issued to Reynolds, which is incorporated by reference herein in its entirety, discusses the use of thermometer codes in binary-weighted DACs. The arrangement of the current sources in the binary-weight DAC array affects the precision of the DAC. For example, fluctuations in threshold voltages and carrier charge mobility cause random mismatches between current sources. Additionally, gradients in oxide thickness, mechanical stress, and resistive voltage drops in supply lines cause linear, parabolic, and higher order gradients across the current source array.
U.S. Pat. No. 6,720,898 issued to Ostrem, which is incorporated by reference herein in its entirety, discloses a layout for a current source array of a binary-weighted DAC for minimizing parabolic errors as well as third harmonic distortions. However, the layout set forth by Ostrem may only be applied to two-dimensional current cell arrays and requires complex routing.
Accordingly, an improved layout and method for binary-weighted DACs are desirable.